It is well known for mobile stations operating in a wireless communication system to monitor their location. An estimate of the current location of each mobile station may be obtained by use in the mobile station of a dedicated location receiver. Such a receiver may detect radio signals from satellites in a known orbit and thereby compute an estimation of the mobile station's current location. A well known example of such a receiver is a GPS receiver. Alternatively, the mobile station may receive signals from at least three fixed transmitters of known position such as transmitters of base stations of a cellular system. The distances from the respective transmitters to the mobile station can be estimated from the times of arrival of the signals from the transmitters. The current location may then be estimated by triangulation.
It is also well known for mobile stations to send to a designated location server within the system regular report messages each giving data describing the current location of the mobile station. The location of all mobile stations within the system may thereby be tracked. Data describing the current location of the mobile stations may be used in known data processing applications running in the system or externally to the system. For example, where the system is a cellular communication system operated by an emergency force such as the police, fire service or ambulance service, location data centrally available at or from a location server from mobile stations operated by users who are personnel belonging to the force allows efficient deployment of such personnel in emergency situations.
Normally, where a mobile station sends location data reports it is usual for the mobile station to send such reports with a fixed periodicity. In connection with the present invention, it has been recognised that in some situations regular periodic reporting of location data to a designated location server by every mobile station in the system may have disadvantages. For example, where mobile stations are located close together, there may be unnecessary use of system wireless resources to send essentially the same location data. Also, an operator using the system to monitor and manage deployment of personnel may have unnecessary work in monitoring mobile stations being used by personnel located close together. Furthermore, in some mobile stations there may also be unnecessary consumption of electrical energy in the usual periodic transmission of regular location data reports, thereby causing an undesirable drain on a battery or other electrical energy source powering the mobile station.
Skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.